This invention concerns refrigeration or air conditioning compressor units of the hermetically sealed type wherein the compressor housing or “shell” encloses the compressor, its drive motor and accessories. In particular, the invention concerns suction gas feed systems utilizing a motor cap as a suction intake to provide gas to the compressor.
Hermetically sealed compressors of the reciprocating type typically incorporate a compressor assembly which encloses the pistons, cylinders, and related compressor parts. A piston crankshaft typically extends from one end of the assembly, and is attached to a motor rotor of an electric motor. One or more stators are provided in proximity to the rotor, with an air gap formed between the rotor and the stator. Setting of this air gap is important to provide proper motor performance for suction and compressor operation in most compressors. In addition, suction gas feed systems often employ a suction gas intake plenum from which conduits convey the gas to the intake mechanism of the compressor assembly such as suction valving for the cylinders. Some examples of such systems are shown in U.S. Pat. Nos. 4,105,374; 4,174,189; 4,236,092; 4,239,461; 4,412,791; 4,503,347; 4,591,318, and 5,538,404.
The suction gas intake plenum may be provided by a number of assemblies and methods. In hermetic compressors, the intake plenum is often provided by a motor cap or shroud (hereinafter “motor cap”) covering the end of the driving motor opposite the shaft. Where a motor cap is provided, it is necessary to provide an inlet or opening in the motor cap to facilitate gas intake for suction by the compressor. Use of a motor cap provides several advantages, such as cooling the motor by directing suction gas across the motor, as well as attenuating suction noise such as from pressure pulses produced by the compressor. For additional sound attenuation, it is well known that suction mufflers or other noise attenuators can be mounted in-line in the suction conduit systems, as shown in U.S. Pat. Nos. 3,101,891; 3,645,358; 3,864,064; 4,239,461; and 5,538,404. The utility disclosures of the above-listed patents are incorporated herein by reference.
However, the prior constructions of suction gas feed assemblies do not provide a high degree of noise attenuation and efficient performance. For example, where motor caps are provided, they are primarily cylindrical in shape, which shape produces the undesirable result of providing excess volume in undesirable areas of gas flow that results in increased superheat and poor motor cooling. Superheat occurs when the suction gas temperature is elevated above the desired temperature, and can be caused by the gas absorbing too much heat from the motor before returning to the compressor. Superheat results in inefficiency in compression since more energy must be expended to lower the elevated gas temperature. The flexibility of the cylindrical shape of known motor caps also results in insufficient stiffness which produces increased noise radiation, and which compromises performance when the motor cap is used as a transportation stop within the top of the compressor assembly. In addition to poor stiffness and poor sound insulation properties, the substantially flat top walls of known cylindrical motor caps also require flat top compressor shell housings, which housings exhibit low stiffness and provide an undesirably high surface areas for sound transmission.
Therefore, what is needed is an improved construction and assembly of suction gas feed assemblies in compressors, particularly in small hermetically sealed, reciprocating units. What is further needed is a motor cap which provides strong suction, minimized superheat, and adequate motor cooling, while providing increased structural stiffness and decreased sound radiation.